There is an adaptive cruise control (ACC) system that automatically controls an inter-vehicle distance between an own vehicle and a leading vehicle by detecting an inter-vehicle distance between the own vehicle and the leading vehicle using a ranging sensor, such as a laser radar. For example, Patent Document 1 discloses a technique of performing ACC by detecting an inter-vehicle distance between the own vehicle and the leading vehicle using a laser radar or a millimeter-wave radar.
Patent Document 1 also discloses, as a method of detecting an inter-vehicle distance between the own vehicle and one other vehicle, a method of utilizing a satellite positioning system, such as a GPS (Global Positioning System), and vehicle-to-vehicle communications as well as problems of this method. According to this method, a location of the other vehicle positioned by a receiver of the satellite positioning system installed to the other vehicle is obtained by vehicle-to-vehicle communications. Then, an inter-vehicle distance between the own vehicle and the other vehicle is obtained by calculating a distance between a location of the own vehicle positioned by a receiver of the satellite positioning system installed to the own vehicle and the location of the other vehicle obtained by vehicle-to-vehicle communications.
Patent Document 1 discloses that the method of detecting an inter-vehicle distance using the satellite positioning system and vehicle-to-vehicle communications has a problem that an error is significant in comparison with a method using a ranging sensor. The technique disclosed in Patent Document 1 therefore uses a value of an inter-vehicle distance calculated by a ranging sensor, such as a laser radar and a millimeter-wave radar, as a value of an inter-vehicle distance between the own vehicle and the leading vehicle.
Patent Document 1: JP-A-2007-280060
In comparison with the method using a satellite positioning system and vehicle-to-vehicle communications, the method of detecting an inter-vehicle distance between the own vehicle and the leading vehicle using a ranging sensor can detect an inter-vehicle distance between the own vehicle and the leading vehicle precisely. However, not all the vehicles are equipped with a ranging sensor, such as a laser radar, and the technique in the related art therefore has a problem that the technique lacks versatility.
Also, even when a vehicle is equipped with a ranging sensor, the vehicle may fail to detect an inter-vehicle distance between the own vehicle and the leading vehicle using the ranging sensor depending on cruising environments, such as a case where a probing wave from the ranging sensor misses the leading vehicle on a curve or slope. In a case where the vehicle fails to detect an inter-vehicle distance between the own vehicle and the leading vehicle using the ranging sensor, an inter-vehicle distance detected using a satellite positioning system and vehicle-to-vehicle communications may be used instead. However, as has been described above, an error is significant with the method using a satellite positioning system and vehicle-to-vehicle communications in comparison with the method using the ranging sensor. Hence, there arises a problem that detection of an inter-vehicle distance between the own vehicle and the leading vehicle becomes less accurate.